Electric melting furnace



Sept. 15, 1953 s. E. GYNT ETAL 2,652,441

ELECTRIC MELTING FURNACE Filed July 7, 195o s sheets-sheet 2 c 23 a 7 /6 /7 fse f4 5 f6. f4 f4 #7514A 7L Lili i E-E A f M fp ,c-

Patented Sept. 15, 1953 ZEZAii ELECTRIC MELTING FURNACE Sven E. Gynt, Vagn Poulsen, and Ragnar Lundqvist, Vasteras, Sweden, assignors to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application .luly 7, 1950, Serial No. 172,434 In Sweden July 22, 1949 6 Claims.

In electric melting furnaces of different kinds it has been proposed to stir the charge by inducing in it electric currents having a comparatively low frequency, i. e. having a frequency of about 1 period per second or less. In order to achieve a suitable stirring, the induction of the currents is performed by a plurality of in relation to each other displaced fields and suitably thereby that below the bottom of Ythe furnace a multiphase winding is arranged which is traversed by a low frequency current. This winding is suitably designed as a winding in an electric generator with coils disposed in slots in an iron core. The bottom of the furnace is then made of a non-magnetic material having a large electric resistance, so that the magnetic force lines can penetrate the bottom of the furnace and its lining without obstruction.

Due to the low frequency used, the iron core in which the coils are disposed may be piled up of heavy sheets, and hitherto the slots for the coils have been cut out in the upper edge of the sheets, i. e. in the edge nearest to the bottom of the furnace.

The present invention concerns an arrangeiron core arranged below the bottom of the furnace, said core being made by rather heavy sheets of which some project above the others, so that the said troughs or bars only in certain points will be in metallic contact with the core. By this fact and thereby that between the troughs and the bottom of the furnace there is a free space, it becomes possible to attain an effective cooling of the iron core and the coils and of the bottom of the furnace by means of air which is forced up across the sheets of the iron core against the coils and the troughs in which these are disposed.

The invention is most readily understood reference being made to the accompanying drawings on which Fig. l shows a cross section through the arrangement according to the invention along the line B-B, and Fig. 2 shows a view of the arrangement seen from above.

Fig. 3 shows a part `of a section along the line G-C- in Fig. 1. Fig. 4a is a section across the winding along the line E-E of Fig. 3 and Fig. 4B is a cross-section through the winding along the line F-F of Fig. 3. Fig. 5 shows the troughs in which the winding is located and also the bars which serve to press down the winding in the trough, everything seen from above. Figs. 6 and '7, finally, show a section through the arrangement along the lines G--G and H-H, respectively, in Fig. 1.

On the drawings, I designates the lining of the furnace and 2 the molten charge, and 3 is the bottom of the furnace below the lining, which bottom is made of some non-magnetic material. li designates the winding coils and 5 the metal caps surrounding the ends of the winding coils, and G is a connection for a pipe line for the delivery of cooling air to the arrangement.

As it will be seen from Figs. 3 and 4, the winding coils consist of copper conductors 'I wound on edge surrounded by a comparatively thin insulation and disposed in short U-shaped bars of iron 8, the channels of which extend perpendicularly to the thick sheets il, I9 and |91 forming the iron cores II, I2 and I3, Figs. 6 and '7. The sheets IE) and Il project above the sheets 9 so that the bars 8 will be carried by the sheets I9 and Il and the webs of the bars are joined with these sheets in one point, either by welding or by a screw connection. The coils 'i are pressed down in the bars by means of fiat strips or bars I which in their turn are forced downwards by means of at bars I5 extending along the bars t, which are insulated from the bars Hl by means of insulation ribs I6 made for instance of hard paper. The bars I5 are pressed against the bars It by means of screws Il with nuts I3. The screws I'I are provided with an insulating sleeve I9 and an insulating washer 2i) resting against the lower side of the bars 8, and below the washer 26 there is a thick metal washer ZI and a lengthways extending sheet 22 for the guidance of the cooling air. The screws il are suitably arranged at connection points between the bars 8, and between the screws II the bars I5 are provided with slots 23, Figs. 4 and 5, through which the cooling air flowing below the bars 8 can escape against the bottom of the furnace.

In order to attain an even cooling of the coils and the bars in which they are disposed, and of the sheet blocks forming the cores, the outermost sheets Il in the sheet blocks are extended down to the bottom of the caps 5 surrounding the ends of the coils. The space which in this way is formed between the sheets |01 and the bottom 51 is divided into four compartments 24, 28, 29 and by means of a vertical intermediary wall 52 (Fig. 1) and two oblique intermediary walls 53 and 54, Figs. 6 and 7, respectively.

The cooling air entering through the pipe line is divided into two currents, one current going to the right in Fig. 1 into that space which in Fig. 6 is designated by 24, and flows from this space through the openings 25 into the space 26 (to the right in Fig. 6) and then flows in intimate contact with the ends of the coils to the opposite end of this space, where it through the openings 21 (Fig. '7 to the right) flows into the space 28 and therefrom into the space between the iron cores Il, I2 and i3 and the lower side of the bars 3 and finally between these and out through the slots 23 against the bottom of the furnace 3. This air current will thus mainly cool the bars to the left of the middle line, Fig. 1. The other part of the cooling air coming from the line 3 flows `first to the left through the space 29 (Fig, 7) and through the openings 33 against the ends of the coils on this side of the winding, and then through the space 3i and through the openings 32 into the space 33 and from this space mainly across the bars 8 on the right side of the middle line (Fig. 1) against the bottom of the furnace.

We claim as our invention:

1. In an electric arc melting furnace, laminate iron cores disposed below the bottom of the furnace and composed of comparatively thick iron sheets disposed in parallel planes, U-shaped iron bars having Webs and channels, the channels of the bars extending transversely of the planes of said sheets and their webs being supported thereon, a multipliase winding having its coil sides disposed in the channels of said bars, and means insulating said coil sides from said bars.

2. In a furnace as claimed in claim 1, some of said sheets extending beyond the other sheets,

4 and the webs of said bars contacting only such extending sheets.

3. In a furnace as claimed in claim 2, means securing each bar to one sheet only.

4. In a furnace as claimed in claim 1, each bar being composed of a plurality of aligned, separate parts insulated from each other.

5. In a furnace as claimed in claim 4, some of said sheets extending beyond the other sheets, and the webs of each of said bar parts contacting only one extending sheet.

6. In a furnace as claimed in claim l, some of said sheets projecting above the other sheets and the Webs of said bars contacting only such projecting sheets, bars of insulating material covering the coil sides in said channels, and holding strips extending above adjacent channel bars to press down said insulating bars ofv two adjacent channel bars.

SVEN E. GYNT. VAGN POULSEN. RAGNAR LUNDQVIST.

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